Photo-electric relay apparatus



Feb. 19, 1935.

w. D. COCKRELL 1 ,992,055

PHOTOELECTRIC RELAY APPARATUS Filed June 29, 1932 Inventor:

VSfil-liam D. Cockrel l,

His A tt orneg.

Patented Feb. 19, 1935 UNITED STATES PATENT OFFICE PHOTO-ELECTRIC RELAYAPPARATUS William D. Cockrell, Schenectady, N. Y., assignor to GeneralElectric Company, a corporation of New York Application June 29, 1932,Serial No. 619,920

Claims. (01. 250-415) In the single figure of the drawin which is acircuit diagram illustrating my invention, leads land 2 represent asource of supply of alternating current which for example may be at 110volts, 60 cycles. Connected across these leads is the are or vaporelectric discharge device 3 having the anode 4, the cathode 5, and thecontrol grid 6. In the anode circuit of'this device is the load device'1 to be controlled thereby which in the present case is illustrated asa relay arranged to control the circuit 8 through its moving contact 9.The cathode 5 is'supplied with heating current from the. secondarywinding 10 of the transformer whose primary 11 connects across thesupply circuit 1, 2, the midpoint ofthe secondary 10 being connectedwith the lead. 2. The charge on the grid 6 of the vapor electric device3 is controlled by the photo-electric device 14, such for example as aphoto-electric tube which is connected in shunt with a portion of thevoltage divider 15. Inasmuch as the device 3 is an are or vapor electricdischarge device it is desirable that it should be caused to passcurrent by the photo-electric device at the beginning of that half cycleupon which it operates rather than at some later time in the half cycle.For this reason I have provided the out-of-phase voltage divider 15which includes the-capacitor 16, which for example may have a .value of.5 mid, the resistors 17, 18 and 19, whose values may be respectively1000 ohms, 2000 ohms and 1000 ohms, the potentiometer 20 which may havea total resistance of 1000 ohms and the secondary winding 21 which maybe wound to produce 30 volts. It will be seen that by reason of thepresence of the capacitor 16 in the voltage divider the current flowingin the divider will lead the voltage of the supply circuit, the amountof lead being suflicient when the photo cell is exposed to light tosupply the grid 6 with a charge such as to 50 cause the device 3 to passcurrent at the instant the supply voltage passes beyond the zero value.

With the photo-electric device connected directly across a portion ofthe voltage divider, for example, between the potentiometer 20 and thepoint 23, I have found that with no light on the photo tube or at leastwith insuflicient light thereon to cause the passage of current throughthe device 3 operation of that device will sometimes occur due totransient or harmonic impulses at the instantthat the supply voltagebegan to rise 5 from the zero value. Since the supply voltage at thistime is but slightly above the zero value, I havetermed this voltage assubstantially zero. To overcome such undesired operation oi device 3, Ihave provided the secondary winding 21 which 10 is arranged to producecurrent flow in. the voltage ,divider 15 in the same direction as thatproduced therein by the potential difference between the supply leads 1and 2, and in the connection between the photo-electric device 14 andthe point 5 23 of the voltage divider I have provided the smallcapacitor 24. which for example may have a value of .0001 mfd.Preferably though not necessarily this capacitor is shunted by theresistor 25 which may have a value of 10 megohms. 20

In the operation of the above described apparatus if a beam of lightfalls upon the photo tube 14 its resulting decrease in resistancesupplies a positive charge to the grid 6 to cause the operation of thedevice 3 at the beginning of each 2 positive half cycle, or in otherwords at the beginning of each half cycle at which the anode 4 is madepositive with respect to the cathode. Current therefore flows throughthe load device 7 through each positive half cycle as long as the photodevice is exposed to light. When the photo device is dark there will bea suflicient grid current because of the secondary 21 during eachnegative half cycle of the supply voltage to produce a charge on thecapacitor 24, that side 5 of the capacitor which connects with the gridbeing left with a negative charge. This charge although small is enoughnevertheless to maintain the grid 6 sumciently negative after the supplyvoltage passes zero and begins the positive half cycle to preventaccidental operation of the device due to transient or harmonicimpulses. It will be understood that after the supply of voltage hasarisen to an appreciable amount in the positive half cycle, that thegrid will be maintained negative by reason of the voltage of thesecondary winding 21 to prevent any undesired operation.

I have chosen the particular embodiment described above as illustrativeof my invention and it will be apparent that various other modificationsmay be made without departing from the spirit and scope of my inventionwhich modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination, a source of alternating current, a load deviceconnected to be supplied from said source, a grid controlled vaporelectric discharge device connected to control the current taken by saidload device, aphoto-electrlc device, means for producing from saidsource a voltage which leads the voltage of the source, means forsupplying said voltage to the grid through said photo-electric deviceand means for supplying a negative voltage to said grid from said sourcewhen the voltage of the source is substantially zero.

2. In combination, a source of alternating current supply, a vaporelectric discharge device having a control grid and a load circuitconnected across said supply, a voltage divider across said supplyconstructed to advance the phase of the current therein, photo-electricdevice connect- :iiig divider with grid and charge to said eubstan rentsupply, a vapor electric discharge having control grid end load circuitconnect 1 divider across ing said divider with said grid and meanscomprising a transformer and a capacitor for supplying a negative chargeto said grid when the voltage of said alternating current supply issubstantially zero.

4. In combination, a source of alternating current supply, a vaporelectric discharge device having a control grid and a load circuitconnected across said supply, a transformer excited from said source ofsupply, a voltage divider connected across said supply and including acapacitor and the secondary of said transformer, photoelectric deviceconnected between said divider and said grid, and a capacitor connectedbetween said grid and said divider.

In combination, a source ol' alternating cur-- ply, vapor," electric cergo device ilith a contro or and cepaci 1or EOlllllEU' di ist

